Snorre Field was discovered by Saga Petroleum (acquired by Norsk Hydro in 1999) in 1979, and came on stream in August 1992. Development of the southern part of the field was aided by a 3-D seismic survey shot in 1983 and another in 1997 for reservoir characterization. This paper describes how Saga used these surveys (known as GE83 and SG9701, respectively) to determine the value of time-lapse seismic data for field management.

Snorre Field is on the Tampen Spur in the Norwegian sector of the Northern North Sea (Figure 1). There are two main reservoirs—the Triassic Lunde Formation and the Triassic-Jurassic Statfjord Formation (Figure 2). Each reservoir consists of a network of fluvial sand bodies in a mudstone matrix, deposited in an alluvial setting. The field has a structural/stratigraphic trap, formed by westward tilting and erosion of a major fault block. Total stratigraphic thickness of the reservoir is more than 1000 m, and 17 zones with varying fluvial styles and complexities have been identified. Both Statfjord and Lunde reservoirs are truncated by the Kimmerian unconformity and overlain by Jurassic and Cretaceous shales. The field is estimated to contain 3.5·109 bbl of undersaturated oil in place, of which approximately 70% occurs in Lunde Formation. Production strategy has mainly been WAG (water alternating gas) injectors and conventional water injectors. Sand connectivity and flow directions are difficult to predict due to the complex geology. Reservoir layers start at approximately 2.4 s on a time-processed seismic section.

Figure 1.

Location of Snorre Field in offshore Norway Blocks 34/4 and 34/7.

Figure 2.

Cross-section through Snorre Field.

GE83 was reprocessed in 1995 and showed signs of an oil-water contact reflection in some parts of the field. Also clear amplitude decay occurs in the reservoir at about 2.6 s, around the oil-water contact level. These observations, and other factors, …